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Chapter 6 (CIC) and Chapter 16 (CTCS)

Chapter 6 (CIC) and Chapter 16 (CTCS). Read in CTCS Chapter 16.4-7 Problems in CTCS: 16.23, 25, 27, 31, 33, 35, 37, 41, 45, 57, 49, 51, 59, 61, 63, 65. pH – Power of Hydrogen. As [H + ] increases, the pH decreases Based on logarithmic scale

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Chapter 6 (CIC) and Chapter 16 (CTCS)

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  1. Chapter 6 (CIC) and Chapter 16 (CTCS) • Read in CTCS Chapter 16.4-7 • Problems in CTCS: 16.23, 25, 27, 31, 33, 35, 37, 41, 45, 57, 49, 51, 59, 61, 63, 65

  2. pH – Power of Hydrogen • As [H+] increases, the pH decreases • Based on logarithmic scale • Compared to a pH = 1 solution, a pH = 2 solution is 10x less acidic • An acid has a pH < 7 • A base has a pH > 7

  3. pH of Some Common Solutions Brown, T.L.; LeMay, H.E.Jr.; and Bursten, B.E. Chemistry the Central Science, 8th Edition, Prentice Hall, Upper Saddle River, NJ, 2000, p 602.

  4. Why Do We Bother With pH? • [H+] = 3.4 x 10-6 is too small • p stands for –log and H stands for [H+] • pH = -log [H+] • Neutral solution has [H+] = 1 x 10-7 or pH = 7.0 Q: If [H+] = 3.4 x 10-6, what is the pH? How many sig figs should there be?

  5. Q: What is the [OH-] of this solution? What is the pOH? • Notice that pH + pOH = 14.00 (pKw) • Derived from [H+] [OH-] = 1 x 10-14 (Kw)

  6. Strong Acids/Bases • Table 4.2 lists these as: • Note that the strong bases are all of the soluble hydroxides

  7. What’s the definition of a strong acid or base? Q: What is the pH of 0.008 M HCl? Q: The pH of the HCl soln in lab was about 1.85. What was it’s concentration?

  8. Q: What is the [OH-] in 0.010 M Sr(OH)2? Q: What is the pH of this solution? Q: What is the pH of a saturated Ca(OH)2 solution if the solubility is 0.97 g/100. mL?

  9. Weak Acids • Not to be confused with dilute acids! • 0.0001 M HCl is NOT a weak acid! HClO + H2O  H3O+ + ClO- • Remember that K = [products]/[reactants]

  10. If [HClO] = 1.0 M, then [H3O+][ClO-] = 3.0 x 10-8 So, since there should be equal amounts of [H3O+] and [ClO-], then [H3O+]2 = 3.0 x 10-8 Or [H3O+] = 1.7 x 10-4 And pH = 3.76

  11. Things to Remember • A Ka must have H+ in the products • Ka’s of strong acids have large values (greater than 1) • A Kb must have OH- in the products • Kb’s of strong bases have large values (greater than 1) • You may not be able to simplify the problem so much and you will have to make approximations

  12. Q: Calculate the pH of a 0.025 M lactic acid solution if its’ Ka = 1.4 x 10-4. A: 2.75

  13. Q: Calculate the Ka of a 0.085 M phenylacetic acid solution if its’ pH is 2.68. A: 5.3 x 10-5

  14. Q: Calculate the pH of a 1.0 M methylamine solution if its’ Kb = 4.38 x 10-4. A: 12.32

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